1. Field of the Invention
The present invention relates to an electric wave receiving apparatus that receives an electric wave modulated by a time code and an electric wave clock that performs the time correct of an internal clock on the basis of a received time code.
2. Related Art
There has been an electric wave clock for receiving a time code to automatically correct the internal clock of the electric wave clock before. The time code is transmitted as a standard electric wave by performing the amplitude modulation (AM) of a carrier wave of 40 kHz or 60 kHz. As shown in FIG. 6, in the time code, a frame of data is composed of 60 data pulses arranged in each second which data pulses are classified into three kinds that are identified by their pulse widths. Then, for example, the time code in Japan is configured so as to express a “minute” by the partial data from 1 second to 8 seconds, an “hour” by the partial data from 12 seconds to 18 seconds, a “total days” by the partial data from 22 seconds to 33 seconds, and a “year” by the partial data from 41 seconds to 48 seconds.
Conventional electric wave clocks have generally received the time code during the whole period of one frame or a plurality of frames of the time code to perform time setting and time corrections (see, for example, US 2007/0177690 A1).
The reception processing of the standard electric wave consumes comparatively large electric power. In particular, in a wrist watch driven by a small-sized battery, the electric power consumption is the level of consumption that cannot be treated lightly. Consequently, there is the problem of shortening a total time during which electric power is consumed by the electric wave receiving processing at the time of receiving the time code to perform a time correction.
Moreover, the standard electric wave sometimes cannot be received as a neat signal owing to attenuation in an office building, the mixture of external noises, and the like. Consequently, there is also the problem of judging the time code accurately to enable a correct time correction even under such a bad electric wave condition.